Joined
·
3,417 Posts
Inspired by LS' descrition of his Pre-Add based Talbot Lago, I prepared a Ferrari 4.5 L for last year's Las Vegas meet. Following his lead, I built it on a brass chassis with a front mounted motor and used a typical spring coupling beteen the motor and the pinion shaft. About half way through the race, run on the Blue King, I heard the characteristic whine of metal spinning on metal and found my car proceeding, very slowly, along the main straight. The diagnosis was clear - the spring was spinning on the pinion shaft. A drop of CYA served as a temporary fix but enough time was lost so that the car finished at or near the bottom of the heap.
I have never been particulary successful in using these couplings outside of their as-manufactured installations - perhaps my home built alignment is less than perfect or my shafting is a poor match for the spring but, in any event, I have found them to be difficult to assemble and unreliable. The Ferrari was prepared with the long track in mind so it mounted a TSRF motor and had a heavy brass chassis - i.e. significant stress on the joint.
In a post re preparation for the Marconi Proxy, Larry Geddes showed his front-engined car with a coupling joint made up from a socket head cap screw and a ball-end Allen wrench. The cap screw was drilled to fit the motor shaft and the wrench was turned down to form the pinion shaft - brilliant - and, as it turns out, based on the Marconi results, very effective.
AS Tom Leherer sang: "Plagarize, plagarize, plagarize, let no on else's work evade your eyes" - so I copied it.
My usual source, McMaster Carr, supplied the cap screws and wrenches. The cap screw was chucked in the 3 jaw on my Unimat and drilled 2mm then the threads turned off and the head cut down (cosmetic -doesn't affect function) The wrench was cut and chucked close in the 3 jaw and a short section, about 4 mm, was turned down to shaft size. A bearing from a defunct motor was chucked in the tailstock and used as a support so the shaft could be further turned, leaving a shoulder to define the position of a flanged ball bearing.
Chassis with socket end on motor and pinion shaft before assembly:
![]()
Close-up:
![]()
and assembled:
![]()
How does it work? - for race performance - we'll see - but there is one measurement that is interesting - using current draw as a measure of load, I observed the following:
Motor alone - uncoupled: 0.25A @ 6 V
Motor + spring and pinion shaft (no crown gear) 0.34A @ 6V
Motor + new joint and pinioin shaft (no crown ) 0.27 A @ 6V
This suggests to me that (1) the motor/pinion shaft alignment is not perfect and (2), in the case of (1), the new joint is more efficient and has less loss than the spring. It is also much easier to assemble since the parts just slide together.
Without any permission, license or endorsement from Larry, I propose to call this the Geddes Joint - after all, we have Chapman struts, deDion rear ends and Prof Fate has attached his nom de guerre to a hinged front axle and I think that this innovation should be similarly recognized.
EM
I have never been particulary successful in using these couplings outside of their as-manufactured installations - perhaps my home built alignment is less than perfect or my shafting is a poor match for the spring but, in any event, I have found them to be difficult to assemble and unreliable. The Ferrari was prepared with the long track in mind so it mounted a TSRF motor and had a heavy brass chassis - i.e. significant stress on the joint.
In a post re preparation for the Marconi Proxy, Larry Geddes showed his front-engined car with a coupling joint made up from a socket head cap screw and a ball-end Allen wrench. The cap screw was drilled to fit the motor shaft and the wrench was turned down to form the pinion shaft - brilliant - and, as it turns out, based on the Marconi results, very effective.
AS Tom Leherer sang: "Plagarize, plagarize, plagarize, let no on else's work evade your eyes" - so I copied it.
My usual source, McMaster Carr, supplied the cap screws and wrenches. The cap screw was chucked in the 3 jaw on my Unimat and drilled 2mm then the threads turned off and the head cut down (cosmetic -doesn't affect function) The wrench was cut and chucked close in the 3 jaw and a short section, about 4 mm, was turned down to shaft size. A bearing from a defunct motor was chucked in the tailstock and used as a support so the shaft could be further turned, leaving a shoulder to define the position of a flanged ball bearing.
Chassis with socket end on motor and pinion shaft before assembly:
Close-up:
and assembled:
How does it work? - for race performance - we'll see - but there is one measurement that is interesting - using current draw as a measure of load, I observed the following:
Motor alone - uncoupled: 0.25A @ 6 V
Motor + spring and pinion shaft (no crown gear) 0.34A @ 6V
Motor + new joint and pinioin shaft (no crown ) 0.27 A @ 6V
This suggests to me that (1) the motor/pinion shaft alignment is not perfect and (2), in the case of (1), the new joint is more efficient and has less loss than the spring. It is also much easier to assemble since the parts just slide together.
Without any permission, license or endorsement from Larry, I propose to call this the Geddes Joint - after all, we have Chapman struts, deDion rear ends and Prof Fate has attached his nom de guerre to a hinged front axle and I think that this innovation should be similarly recognized.
EM
